CONTROL SYSTEM FOR HVAC SYSTEM

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 63/650,335, entitled “CONTROL SYSTEM FOR HVAC SYSTEM,” filed May 21, 2024, which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Heating, ventilation, and/or air conditioning (HVAC) systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature and humidity, for occupants of the respective environments. An HVAC system may control environmental properties by controlling a supply air flow delivered to the environment. For example, the HVAC system may place the supply air flow in a heat exchange relationship with a refrigerant of a vapor compression circuit to condition the supply air flow. Some thermostats (e.g., communicating thermostats) may provide command data to enable variable operation of certain components of the HVAC system. Other thermostats (e.g., non-communicating thermostats) may provide a simple switching command to the components instead. Thus, operation and/or performance of the HVAC system may be limited when certain thermostats are utilized with the HVAC system.

SUMMARY

In an embodiment, a heating, ventilation, and/or air conditioning (HVAC) system includes a thermostat configured to generate a thermostat signal to control a vapor compression system based on a difference between a temperature setpoint and a measured temperature. The HVAC system further includes control circuitry configured to receive the thermostat signal and to determine a target evaporator temperature based on the thermostat signal. Further, the control circuitry is configured to adjust a compressor speed of a compressor based on a difference between the target evaporator temperature and a measured evaporator temperature.

In another embodiment, a method of controlling a heating, ventilation, and/or air conditioning (HVAC) system includes receiving, via control circuitry, a thermostat signal from a thermostat indicative of an instruction to operate a vapor compression system. Additionally, the method includes determining, via the control circuitry, a target evaporator temperature based on the thermostat signal. Furthermore, the method includes generating, via the control circuitry, a control signal to control a compressor speed of a compressor based on a difference between the target evaporator temperature and a measured evaporator temperature.

In another embodiment, a heating, ventilation, and/or air conditioning (HVAC) system includes control circuitry configured to operate in a first mode when connected to a communicating thermostat and configured to operate in a second mode when connected to a non-communicating thermostat. In the first mode, the control circuitry is configured to receive digital communication from the communicating thermostat, determine a target evaporator temperature based on the digital communication, and adjust a compressor speed of a compressor based on the target evaporator temperature. In the second mode, the control circuitry is configured to receive an activation signal from the non-communicating thermostat, set the target evaporator temperature to a predetermined value associated with the activation signal, and adjust the compressor speed of the compressor based on the target evaporator temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a building incorporating a heating, ventilation, and/or air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure;

FIG. 2 is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure;

FIG. 3 is a perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure;

FIG. 4 is a schematic diagram of an embodiment of a vapor compression system used in an HVAC system, in accordance with an aspect of the present disclosure;

FIG. 5 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a heat pump system, illustrating the heat pump system configured for operation in a heating mode, in accordance with an aspect of the present disclosure; and

FIG. 6 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a heat pump system, illustrating the heat pump system configured for operation in a cooling mode, in accordance with an aspect of the present disclosure;

FIG. 7 is a block diagram of an embodiment of a control scheme of an HVAC system in accordance with an aspect of the present disclosure;

FIG. 8 is a block diagram of a vapor compression system of an HVAC system in accordance with an aspect of the present disclosure;

FIG. 9 is a block diagram of a control scheme for controlling a compressor, in accordance with an aspect of the present disclosure;

FIG. 10 is a block diagram of a room control loop, in accordance with an aspect of the present disclosure;

FIG. 11 is a block diagram of a compressor control loop, in accordance with an aspect of the present disclosure;

FIG. 12 is a block diagram of an EEV control loop in accordance with an aspect of the present disclosure;

FIG. 13 is a block diagram of an injection EEV control loop in accordance with an aspect of the present disclosure; and

FIG. 14 is a block diagram of a fan control loop in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

As used herein, the terms “approximately,” “generally,” and “substantially,” and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being “approximately” equal to (or, for example, “substantially similar” to) a given value, this is intended to mean that the property value may be within +/−5%, within +/−4%, within +/−3%, within +/−2%, within +/−1%, or even closer, of the given value. Similarly, when a given feature is described as being “substantially parallel” to another feature, “generally perpendicular” to another feature, and so forth, this is intended to mean that the given feature is within +/−5%, within +/−4%, within +/−3%, within +/−2%, within +/−1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Further, it should be understood that mathematical terms, such as “planar,” “slope,” “perpendicular,” “parallel,” and so forth are intended to encompass features of surfaces or elements as understood to one of ordinary skill in the relevant art, and should not be rigidly interpreted as might be understood in the mathematical arts. For example, a “planar” surface is intended to encompass a surface that is machined, molded, or otherwise formed to be substantially flat or smooth (within related tolerances) using techniques and tools available to one of ordinary skill in the art. Similarly, a surface having a “slope” is intended to encompass a surface that is machined, molded, or otherwise formed to be oriented at an angle (e.g., incline) with respect to a point of reference using techniques and tools available to one of ordinary skill in the art.

A heating, ventilation, and/or air conditioning (HVAC) system may be used to thermally regulate a space within a building, home, or other suitable structure. For example, the HVAC system may include a vapor compression system that transfers thermal energy between a working fluid, such as a refrigerant, and a fluid to be conditioned, such as air. The vapor compression system includes heat exchangers, such as a condenser and an evaporator, which are fluidly coupled to one another via one or more conduits of a working fluid loop or circuit (e.g., refrigerant circuit). A compressor may be used to circulate the working fluid through the conduits and other components of the working fluid circuit (e.g., an expansion device) and, thus, enable the transfer of thermal energy between components of the working fluid circuit (e.g., between the condenser and the evaporator) and one or more thermal loads (e.g., an environmental air flow, a supply air flow). Additionally or alternatively, the HVAC system may include a heat pump (e.g., a heat pump system) having a first heat exchanger (e.g., a heating and/or cooling coil, an indoor coil, the evaporator) positioned within the space to be conditioned, a second heat exchanger (e.g., a heating and/or cooling coil, an outdoor coil, the condenser) positioned in or otherwise fluidly coupled to an ambient environment (e.g., the atmosphere), and a pump (e.g., the compressor) configured to circulate the working fluid (e.g., refrigerant) between the first and second heat exchangers to enable heat transfer between the thermal load (e.g., an air flow to be conditioned) and the ambient environment, for example. The heat pump system is operable to provide both cooling and heating to the space to be conditioned (e.g., a room, zone, or other region within a building) by adjusting a flow of the working fluid through the working fluid circuit. Thus, the heat pump may not include a dedicated heating system, such as a furnace or burner configured to combust a fuel, to enable operation of the HVAC system in the heating mode.

The HVAC system may be configured to operate in various operating modes to condition a supply air flow and to deliver the supply air flow to a space to condition the space. For example, the HVAC system may have a compressor (e.g., in an outdoor unit) that can operate at different (e.g., variable) capacities or stages. Additionally or alternatively, the HVAC system may include a furnace (e.g., a modulating furnace) that can operate at different (e.g., variable) stages or modes. A control system (e.g., a primary control system, a primary control board, primary control circuitry) of the HVAC system may select or adjust the operating mode of the HVAC system to condition the supply air flow more efficiently or effectively, such as based on various operating parameters (e.g., a set point temperature) associated with the HVAC system.

In existing HVAC systems, the control system may be configured to operate the HVAC system in the various operating modes based on signals received from a thermostat. The signals may be indicative of operating parameters used for selecting or adjusting the operating mode of the HVAC system. However, certain thermostats (e.g., non-communicating thermostats) may not provide a portion of the signals typically utilized to adjust variable operation of the HVAC system. As a result, the control system may be unable to operate the HVAC system in various operating modes based on the signals received from such thermostats. For this reason, operation and/or performance of the HVAC system may be limited when certain thermostats are utilized with the HVAC system.

Thus, it is presently recognized that enabling the control system to operate the HVAC system in various operating modes based on signals provided by a conventional or traditional thermostat (e.g., a switching thermostat) may improve operation of the HVAC system. Accordingly, embodiments of the present disclosure are directed to control circuitry (e.g., additional control circuitry, secondary control circuitry) that enables the control system to operate in various operating modes using signals (e.g., electrical signals) transmitted by a traditional or conventional thermostat (e.g., non-communicating thermostat). For example, the control circuitry may provide a predetermined value to be used as a set point for a variable capacity operating parameter. As discussed in further detail below, the value or predetermined value of the operating parameter may be utilized by the control system as a substitute for data that would typically be provided by a communicating (e.g., non-conventional) thermostat. As a result, the control circuitry enables operation of the HVAC system in the various operating modes using signals from conventional, non-communicating thermostats, thereby improving performance of the HVAC system.

Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and/or air conditioning (HVAC) system for environmental management that employs one or more HVAC units in accordance with the present disclosure. As used herein, an HVAC system includes any number of components configured to enable regulation of parameters related to climate characteristics, such as temperature, humidity, air flow, pressure, air quality, and so forth. For example, an “HVAC system” as used herein is defined as conventionally understood and as further described herein. Components or parts of an “HVAC system” may include, but are not limited to, all, some of, or individual parts such as a heat exchanger, a heater, an air flow control device, such as a fan, a sensor configured to detect a climate characteristic or operating parameter, a filter, a control device configured to regulate operation of an HVAC system component, a component configured to enable regulation of climate characteristics, or a combination thereof. An “HVAC system” is a system configured to provide such functions as heating, cooling, ventilation, dehumidification, pressurization, refrigeration, filtration, or any combination thereof. The embodiments described herein may be utilized in a variety of applications to control climate characteristics, such as residential, commercial, industrial, transportation, or other applications where climate control is desired.

In the illustrated embodiment, a building 10 is air conditioned by a system that includes an HVAC unit 12 in accordance with present embodiments. The building 10 may be a commercial structure or a residential structure. As shown, the HVAC unit 12 is disposed on the roof of the building 10; however, the HVAC unit 12 may be located in other equipment rooms or areas adjacent the building 10. The HVAC unit 12 may be a single package unit containing other equipment, such as a blower and/or integrated air handler. In other embodiments, the HVAC unit 12 may be part of a split HVAC system, such as the system shown in FIG. 3, which includes an outdoor HVAC unit 58 and an indoor HVAC unit 56.

The HVAC unit 12 is an air-cooled device that implements a refrigeration cycle to provide conditioned air to the building 10. Specifically, the HVAC unit 12 may include one or more heat exchangers across which an air flow is passed to condition the air flow before the air flow is supplied to the building. In the illustrated embodiment, the HVAC unit 12 is a rooftop unit (RTU) that conditions a supply air flow, such as environmental air and/or a return air flow from the building 10. After the HVAC unit 12 conditions the air, the air is supplied to the building 10 via ductwork 14 extending throughout the building 10 from the HVAC unit 12. For example, the ductwork 14 may extend to various individual floors or other sections of the building 10. In certain embodiments, the HVAC unit 12 may be a heat pump that provides both heating and cooling to the building with one refrigeration circuit configured to operate in different modes.

A control device 16, one type of which may be a thermostat, may be used to designate the temperature of the conditioned air. The control device 16 also may be used to control the flow of air through the ductwork 14. For example, the control device 16 may be used to regulate operation of one or more components of the HVAC unit 12 or other components, such as dampers and fans, within the building 10 that may control flow of air through and/or from the ductwork 14. In some embodiments, other devices may be included in the system, such as pressure and/or temperature transducers or switches that sense the temperatures and pressures of the supply air, return air, and so forth. Moreover, the control device 16 may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building 10.

FIG. 2 is a perspective view of an embodiment of the HVAC unit 12. In the illustrated embodiment, the HVAC unit 12 is a single package unit that may include one or more independent working fluid circuits and components that are tested, charged, wired, piped, and ready for installation. The HVAC unit 12 may provide a variety of heating and/or cooling functions, such as cooling only, heating only, cooling with dehumidification, heating with a heat pump, and/or cooling with a heat pump. As described above, the HVAC unit 12 may directly cool and/or heat an air flow provided to the building 10 to condition a space in the building 10.

As shown in the illustrated embodiment of FIG. 2, a cabinet 24 encloses the HVAC unit 12 and provides structural support and protection to the internal components from environmental and other contaminants. In some embodiments, the cabinet 24 may be constructed of galvanized steel and insulated with aluminum foil faced insulation. Rails 26 may be joined to the bottom perimeter of the cabinet 24 and provide a foundation for the HVAC unit 12. In certain embodiments, the rails 26 may provide access for a forklift and/or overhead rigging to facilitate installation and/or removal of the HVAC unit 12. In some embodiments, the rails 26 may fit into “curbs” on the roof to enable the HVAC unit 12 to provide air to the ductwork 14 from the bottom of the HVAC unit 12 while blocking elements such as rain from leaking into the building 10.

The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more working fluid circuits. Tubes within the heat exchangers 28 and 30 may circulate a working fluid (e.g., refrigerant), such as R-454B and/or R32, through the heat exchangers 28 and 30. The tubes may be of various types, such as multichannel tubes, conventional copper or aluminum tubing, and so forth. Together, the heat exchangers 28 and 30 may implement a thermal cycle in which the working fluid undergoes phase changes and/or temperature changes as it flows through the heat exchangers 28 and 30 to produce heated and/or cooled air. For example, the heat exchanger 28 may function as a condenser where heat is released from the working fluid to ambient air, and the heat exchanger 30 may function as an evaporator where the working fluid absorbs heat to cool an air flow. In some embodiments, the HVAC unit 12 may operate in a heat pump mode where the roles of the heat exchangers 28 and 30 may be reversed. That is, the heat exchanger 28 may function as an evaporator and the heat exchanger 30 may function as a condenser. While the illustrated embodiment of FIG. 2 shows the HVAC unit 12 having two of the heat exchangers 28 and 30, in other embodiments, the HVAC unit 12 may include one heat exchanger or more than two heat exchangers.

The heat exchanger 30 is located within a compartment 31 that separates the heat exchanger 30 from the heat exchanger 28. Fans 32 draw air from the environment through the heat exchanger 28. Air may be heated and/or cooled as the air flows through the heat exchanger 28 before being released back to the environment surrounding the HVAC unit 12. A blower assembly 34, powered by a motor 36, draws air through the heat exchanger 30 to heat or cool the air. The heated or cooled air may be directed to the building 10 by the ductwork 14, which may be connected to the HVAC unit 12. Before flowing through the heat exchanger 30, the conditioned air flows through one or more filters 38 that may remove particulates and contaminants from the air. In certain embodiments, the filters 38 may be disposed on the air intake side of the heat exchanger 30 to prevent contaminants from contacting the heat exchanger 30.

The HVAC unit 12 also may include other equipment for implementing the thermal cycle. Compressors 42 increase the pressure and temperature of the working fluid before the working fluid enters the heat exchanger 28. The compressors 42 may be any suitable type of compressors, such as scroll compressors, rotary compressors, screw compressors, or reciprocating compressors. In some embodiments, the compressors 42 may include a pair of hermetic direct drive compressors arranged in a dual stage configuration 44. However, in other embodiments, any number of the compressors 42 may be provided to achieve various stages of heating and/or cooling. As may be appreciated, additional equipment and devices may be included in the HVAC unit 12, such as a solid-core filter drier, a drain pan, a disconnect switch, an economizer, pressure switches, phase monitors, and humidity sensors, among other components.

The HVAC unit 12 may receive power through a terminal block 46. For example, a high voltage power source may be connected to the terminal block 46 to power the equipment. The operation of the HVAC unit 12 may be governed or regulated by a control board 48. The control board 48 may include control circuitry connected to a thermostat, sensors, and alarms. One or more of these components may be referred to herein separately or collectively as the control device 16. The control circuitry may be configured to control operation of the equipment, provide alarms, and monitor safety switches. Wiring 49 may connect the control board 48 and the terminal block 46 to the equipment of the HVAC unit 12.

FIG. 3 illustrates a residential heating and cooling system 50, also in accordance with present techniques. The residential heating and cooling system 50 may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system 50 is a split HVAC system. In general, a residence 52 conditioned by a split HVAC system may include working fluid conduits 54 (e.g., refrigerant conduits) that operatively couple the indoor unit 56 to the outdoor unit 58. The indoor unit 56 may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit 58 is typically situated adjacent to a side of residence 52 and is covered by a shroud to protect the system components and to prevent leaves and other debris or contaminants from entering the unit. The working fluid conduits 54 transfer working fluid between the indoor unit 56 and the outdoor unit 58, typically transferring primarily liquid working fluid in one direction and primarily vaporized working fluid in an opposite direction.

When the system shown in FIG. 3 is operating as an air conditioner, a heat exchanger 60 in the outdoor unit 58 serves as a condenser for re-condensing vaporized working fluid flowing from the indoor unit 56 to the outdoor unit 58 via one of the working fluid conduits 54. In these applications, a heat exchanger 62 of the indoor unit functions as an evaporator. Specifically, the heat exchanger 62 receives liquid working fluid, which may be expanded by an expansion device, and evaporates the working fluid before returning it to the outdoor unit 58.

The outdoor unit 58 draws environmental air through the heat exchanger 60 using a fan 64 and expels the air above the outdoor unit 58. When operating as an air conditioner, the air is heated by the heat exchanger 60 within the outdoor unit 58 and exits the unit at a temperature higher than it entered. The indoor unit 56 includes a blower or fan 66 that directs air through or across the indoor heat exchanger 62, where the air is cooled when the system is operating in air conditioning mode. Thereafter, the air is passed through ductwork 68 that directs the air to the residence 52. The overall system operates to maintain a desired temperature as set by a system controller. When the temperature sensed inside the residence 52 is higher than the set point on the thermostat, or the set point plus a small amount, the residential heating and cooling system 50 may become operative to refrigerate additional air for circulation through the residence 52. When the temperature reaches the set point, or the set point minus a small amount, the residential heating and cooling system 50 may stop the refrigeration cycle temporarily.

The residential heating and cooling system 50 may also operate as a heat pump. When operating as a heat pump, the roles of heat exchangers 60 and 62 are reversed. That is, the heat exchanger 60 of the outdoor unit 58 will serve as an evaporator to evaporate working fluid and thereby cool air entering the outdoor unit 58 as the air passes over the outdoor heat exchanger 60. The indoor heat exchanger 62 will receive a stream of air blown over it and will heat the air by condensing the working fluid.

FIG. 4 is an embodiment of a vapor compression system 72 that can be used in any of the systems described above. The vapor compression system 72 may circulate a working fluid through a circuit starting with a compressor 74. The circuit may also include a condenser 76, an expansion valve(s) or device(s) 78, and an evaporator 80. The vapor compression system 72 may further include a control panel 82 that has an analog to digital (A/D) converter 84, a microprocessor 86, a non-volatile memory 88, and/or an interface board 90. The control panel 82 and its components may function to regulate operation of the vapor compression system 72 based on feedback from an operator, from sensors of the vapor compression system 72 that detect operating conditions, and so forth.

In some embodiments, the vapor compression system 72 may use one or more of a variable speed drive (VSDs) 92, a motor 94, the compressor 74, the condenser 76, the expansion valve or device 78, and/or the evaporator 80. The motor 94 may drive the compressor 74 and may be powered by the variable speed drive (VSD) 92. The VSD 92 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 94. In other embodiments, the motor 94 may be powered directly from an AC or direct current (DC) power source. The motor 94 may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 74 compresses a working fluid vapor and delivers the vapor to the condenser 76 through a discharge passage. In some embodiments, the compressor 74 may be a centrifugal compressor, a scroll compressor, a screw compressor, a rotary compressor, or any other suitable type of compressor. The working fluid vapor delivered by the compressor 74 to the condenser 76 may transfer heat to a fluid passing across the condenser 76, such as ambient or environmental air 96. The working fluid vapor may condense to a working fluid liquid in the condenser 76 as a result of thermal heat transfer with the environmental air 96. The liquid working fluid from the condenser 76 may flow through the expansion device 78 to the evaporator 80.

The liquid working fluid delivered to the evaporator 80 may absorb heat from another air flow, such as a supply air flow 98 provided to the building 10 or the residence 52. For example, the supply air flow 98 may include ambient or environmental air, return air from a building, or a combination of the two. The liquid working fluid in the evaporator 80 may undergo a phase change from the liquid working fluid to a working fluid vapor. In this manner, the evaporator 80 may reduce the temperature of the supply air flow 98 via thermal heat transfer with the working fluid. Thereafter, the vapor working fluid exits the evaporator 80 and returns to the compressor 74 by a suction line to complete the cycle.

In some embodiments, the vapor compression system 72 may further include a reheat coil. In the illustrated embodiment, the reheat coil is represented as part of the evaporator 80. The reheat coil is positioned downstream of the evaporator heat exchanger relative to the supply air flow 98 and may reheat the supply air flow 98 when the supply air flow 98 is overcooled to remove humidity from the supply air flow 98 before the supply air flow 98 is directed to the building 10 or the residence 52.

It should be appreciated that any of the features described herein may be incorporated with the HVAC unit 12, the residential heating and cooling system 50, or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air flow provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications.

To provide context for the following discussion, FIG. 5 is a schematic of an embodiment of a portion of an HVAC system 100 that includes a heat pump 102 (e.g., a heat pump system, a reverse-cycle heat pump, an energy efficient heat pump) in accordance with present embodiments. The heat pump 102 may include one or more components of the vapor compression system 72 discussed above and/or may be included in any of the systems described above (e.g., the HVAC unit 12, the heating and cooling system 50). The heat pump 102 includes a first heat exchanger 104 and a second heat exchanger 106 that are fluidly coupled to one another via a working fluid circuit 108 or working fluid loop (e.g., one or more conduits, refrigerant circuit). The first heat exchanger 104 may be in thermal communication with (e.g., fluidly coupled to) a thermal load 110 (e.g., a room, space, and/or device) serviced by the heat pump 102, and the second heat exchanger 106 may be in thermal communication with an ambient environment 112 (e.g., the atmosphere, outdoor environment) surrounding the HVAC system 100.

In some embodiments, a first fan 116 (e.g., blower) may direct a first air flow across the first heat exchanger 104 to facilitate heat exchange between working fluid within the first heat exchanger 104 and the thermal load 110, while a second fan 118 may direct a second air flow across the second heat exchanger 106 to facilitate heat exchange between working fluid within the second heat exchanger 106 and the ambient environment 112. Thus, the heat pump 102 may be an air-source heat pump. One or more electronic expansion valves (EEV) 120 (e.g., a bi-directional expansion valve) may be disposed along the working fluid circuit 108 between the first heat exchanger 104 and the second heat exchanger 106 and may be configured to regulate (e.g., throttle) a flow of working fluid and/or a working fluid pressure differential between the first and second heat exchangers 104, 106.

The heat pump 102 also includes a compressor 130 (e.g., compressor system, positive displacement compressor) disposed along the working fluid circuit 108. The compressor 130 is configured to direct working fluid flow through the first heat exchanger 104, the second heat exchanger 106, and remaining components (e.g., the EEV(s) 120) that may be fluidly coupled to the working fluid circuit 108. Although one compressor 130 is shown in the illustrated embodiment, the heat pump 102 may include any suitable quantity of compressors 130, such as two, three, four, five, six, or more than six compressors 130. The compressor 130 may be a fixed speed compressor, a multi-stage (e.g., two stage) compressor, and/or a variable speed compressor. Additionally, the compressor 130 may be a rotary compressor, a scroll compressor, a screw compressor, or any other suitable type of compressor (e.g., high-side shell compressor, positive displacement compressor).

The compressor 130 is configured to receive working fluid (e.g., a primary flow of working fluid) via a suction conduit 132 fluidly coupled to a suction port 134 of the compressor 130 and to discharge working fluid (e.g., compressed working fluid) via a discharge conduit 136 fluidly coupled to a discharge port 138 of the compressor 130. Further, the compressor 130 is also configured to receive an injected flow of working fluid (e.g., a secondary flow of working fluid) via one or more injection ports 140 of the compressor 130, as described in further detail below. As shown, the one or more injection ports 140 may be configured to direct the injected flow of working fluid into the compressor 130 at an intermediate location between the suction port 134 and the discharge port 138 of the compressor 130. That is, the one or more injection ports 140 are configured to direct the injected flow of working fluid into the compressor 130 downstream of the suction port 134 and upstream of the discharge port 138, relative to a flow direction of working fluid through the compressor 130. In some embodiments, the compressor 130 may include multiple injection ports 140 positioned at different intermediate locations along the compressor 130 (e.g., along a working fluid flow path of the compressor 130 from the suction port 134 to the discharge port 138).

The compressor 130 may be fluidly coupled to a remainder of the working fluid circuit 108 via a reversing valve 150 (e.g., a switch-over valve). In the illustrated embodiment, the reversing valve 150 includes a first port 152 that is fluidly coupled to the suction conduit 132, a second port 154 that is fluidly coupled to the discharge conduit 136, a third port 156 that is fluidly coupled to a first conduit portion 158 of the working fluid circuit 108 extending to the first heat exchanger 104, and a fourth port 160 that is fluidly coupled to a second conduit portion 162 of the working fluid circuit 108 extending to the second heat exchanger 106.

The reversing valve 150 is configured to transition between a first configuration 164, in which the reversing valve 150 fluidly couples the first port 152 and the fourth port 160 and fluidly couples the second port 154 and the third port 156, and a second configuration 170 (FIG. 6), in which the reversing valve 150 fluidly couples the first port 152 and the third port 156 and fluidly couples the second port 154 and the fourth port 160. Accordingly, in the first configuration 164, the reversing valve 150 enables the compressor 130 to receive a flow of working fluid (e.g., via the suction port 134) from the second heat exchanger 106 and to discharge a flow of working fluid (e.g., via the discharge port 138) to the first heat exchanger 104. Conversely, in the second configuration 170, the reversing valve 150 enables the compressor 130 to receive a flow of working fluid (e.g., via the suction port 134) from the first heat exchanger 104 and to discharge a flow of working fluid (e.g., via the discharge port 138) to the second heat exchanger 106. In this way, while in the first configuration 164, the reversing valve 150 enables the heat pump 102 to operate in a heating mode, in which the first heat exchanger 104 rejects thermal energy to the thermal load 110 to heat the thermal load and the second heat exchanger 106 absorbs thermal energy from the ambient environment 112. Further, while in the second configuration 170, the reversing valve 150 enables the heat pump 102 to operate in a cooling mode, in which the first heat exchanger 104 absorbs thermal energy from the thermal load 110 to cool the thermal load and the second heat exchanger 106 rejects the absorbed thermal energy (e.g., absorbed from the thermal load 110) to the ambient environment 112. As such, while the reversing valve 150 is in the first configuration 164, the compressor 130 may direct a working fluid flow along at least a portion of the working fluid circuit 108 in a first flow direction 172. While the reversing valve 150 is in the second configuration 170, the compressor 130 may direct a working fluid flow along at least a portion of the working fluid circuit 108 in a second flow direction 174, opposite the first flow direction 172. For clarity, the heat pump 102 (e.g., energy efficient heat pump) is shown configured for operation in a heating mode in the illustrated embodiment of FIG. 5. Moreover, FIG. 6 is a schematic of an embodiment of a portion of the HVAC system 100 illustrating the heat pump 102 (e.g., energy efficient heat pump) configured for operation in a cooling mode.

The present discussion continues with reference to FIG. 5. The heat pump 102 may also include additional components, such as an accumulator 180 and/or a compensator 182. The accumulator 180 is generally configured to enable control of an amount of liquid working fluid circulating in the working fluid circuit 108. For example, the accumulator 180 may enable adjustment in the amount of liquid working fluid circulating in the working fluid circuit 108 in low ambient conditions (e.g., cold temperatures in the ambient environment 112). The compensator 182 may also be configured to enable control of an amount of working fluid circulating in the working fluid circuit 108. For example, the compensator 182 may be configured to retain a portion of working fluid therein during the heating mode of the heat pump 102, such that the portion of retained working fluid does not circulate through the working fluid circuit 108 (e.g., in the first flow direction 172), to improve operation of the heat pump 102 in the heating mode.

As mentioned above, the heat pump 102 is also configured to enable injection of working fluid into the compressor 130. Specifically, present embodiments include the heat pump 102 configured to divert a portion of working fluid within the working fluid circuit 108 and to inject the portion of working fluid into the compressor 130 via the injection port 140 of the compressor 130. To this end, the heat pump 102 (e.g., the working fluid circuit 108) includes an injection conduit 200 extending from a liquid conduit portion 202 (e.g., a third conduit portion) of the working fluid circuit 108 to the injection port 140 of the compressor 130. As shown, the liquid conduit portion 202 extends between the first heat exchanger 104 and the second heat exchanger 106. Thus, working fluid directed through the liquid conduit portion 202 may be in a liquid phase in both the heating mode and cooling mode of the heat pump 102. For example, in the heating mode, the working fluid may flow along the working fluid circuit 108 through (e.g., sequentially through) the first conduit portion 158, the first heat exchanger 104, the liquid conduit portion 202, the second heat exchanger 106, and the second conduit portion 162.

In the heating mode, liquid working fluid may be directed along the liquid conduit portion 202 (e.g., in the first flow direction 172) from the first heat exchanger 104 toward the second heat exchanger 106. As indicated by arrow 204, a portion the working fluid within the liquid conduit portion 202 may be diverted to the injection conduit 200 for injection into the compressor 130 via the injection port 140. The working fluid may be provided to the injection port 140 as a vapor working fluid or as a liquid-vapor mixture of working fluid. To this end, the heat pump 102 includes an injection electronic expansion valve (EEV) 206 disposed along the injection conduit 200. For example, the injection EEV 206 may be an electronic expansion valve (EEV), a modulating valve, a solenoid valve, a fixed orifice, a capillary tube, or a combination thereof. Thus, the injection EEV 206 may operate to reduce a pressure and/or a temperature of (e.g., “flash”) the portion of the working fluid directed from the liquid conduit portion 202 to the injection conduit 200, which may cause the working fluid within the injection conduit 200 to vaporize or partially vaporize. The injection EEV 206 may also be controlled to enable adjustment of the flow of working fluid directed along the injection conduit 200 to the injection port 140 of the compressor 130, as discussed further below.

The HVAC system 100 may also include a controller 220 (e.g., a control system, a thermostat, a control panel, control circuitry, automation controller) that is communicatively coupled to one or more components of the heat pump 102 and is configured to monitor, adjust, and/or otherwise control operation of one or more components of the heat pump 102. For example, one or more control transfer devices, such as wires, cables, wireless communication devices, and the like, may communicatively couple the compressor 130, the EEV(s) 120, the first and/or second fans 116, 118, the control device 16 (e.g., a thermostat), and/or any other suitable components of the HVAC system 100 to the controller 220. That is, the compressor 130, the EEV(s) 120, the first and/or second fans 116, 118, and/or the control device 16 may each have one or more communication components that facilitate wired or wireless (e.g., via a network) communication with the controller 220. In some embodiments, the communication components may include a network interface that enables the components of the HVAC system 100 to communicate via various protocols such as EtherNet/IP, ControlNet, DeviceNet, or any other communication network protocol. Alternatively, the communication components may enable the components of the HVAC system 100 to communicate via mobile telecommunications technology, Bluetooth®, near-field communications technology, and the like. As such, the controller 220, the compressor 130, the EEV(s) 120, the first and/or second fans 116, 118, and/or the control device 16 may wirelessly communicate data between each other. In other embodiments, operational control of certain components of the heat pump 102 may be regulated by one or more relays or switches (e.g., a 24 volt alternating current [VAC] relay).

In some embodiments, the controller 220 may be a component of or may include the control panel 82. In other embodiments, the controller 220 may be a standalone controller, a dedicated controller, or another suitable controller included in the HVAC system 100. In any case, the controller 220 is configured to control components of the HVAC system 100 in accordance with the techniques discussed herein. The controller 220 includes processing circuitry 222, such as a microprocessor, which may execute software for controlling the components of the HVAC system 100. The processing circuitry 222 may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. For example, the processing circuitry 222 may include one or more reduced instruction set (RISC) processors.

The controller 220 may also include a memory device 224 (e.g., a memory) that may store information, such as instructions, control software, look up tables, configuration data, etc. The memory device 224 may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device 224 may store a variety of information and may be used for various purposes. For example, the memory device 224 may store processor-executable instructions including firmware or software for the processing circuitry 222 execute, such as instructions for controlling components of the HVAC system 100 (e.g., the heat pump 102). In some embodiments, the memory device 224 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 222 to execute. The memory device 224 may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The memory device 224 may store data, instructions, and any other suitable data.

In accordance with present techniques, the controller 220 may also be configured to control operation of the injection EEV 206 disposed along the injection conduit 200. In particular, the controller 220 may regulate operation of the injection EEV 206 to control flow of the working fluid through the injection conduit 200 to the injection port 140. Indeed, the injection EEV 206 may be controlled to adjust one or more properties of the working fluid injected into the compressor 130 (e.g., via the injection port 140), such as a flow rate, a temperature, a pressure, a phase, or other attribute of the working fluid. The controller 220 may also regulate operation of the injection EEV 206 to achieve other operating parameters (e.g., target operating parameters) of the heat pump 102. For example, the heat pump 102 may include one or more sensors 226 configured to detect one or more operating parameters of the heat pump 102, and the controller 220 may control operation of the injection EEV 206 (e.g., adjust a position of the injection EEV 206) based on feedback received from the one or more sensors 226. The one or more sensors 226 may be configured to detect any suitable operating parameter associated with the heat pump 102, such as temperature, pressure, flow rate, and so forth.

In some embodiments, one or more of the sensors 226 may be disposed along the discharge conduit 136 and may be configured to detect a temperature and/or a pressure (e.g., operating parameter) of working fluid discharged by the compressor 130. In such embodiments, the controller 220 may control operation of the injection EEV 206 to adjust flow of working fluid injected into the compressor 130 via the injection port 140 to achieve a desired temperature and/or pressure of the working fluid (e.g., desired superheat, desired discharge temperature, desired operating parameter value) discharged by the compressor 130. In some embodiments, the controller 220 may control operation of the expansion valve 206 based on other parameters, such as a speed of the compressor 130, a stage of the compressor 130, an operating mode of the heat pump 102, a set point temperature of a space conditioned by the heat pump 102, a detected temperature of the space conditioned by the heat pump 102, a temperature of the ambient environment 112, and so forth. For example, the controller 220 may be configured to operate the injection EEV 206 to enable injection of working fluid into the compressor 130 via the injection port 140 during operation of the compressor 130 at an upper speed limit (e.g., highest speed, full capacity).

The working fluid within the injection conduit 200 may be injected into the compressor 130 via the injection port 140 to enable improved operation of the heat pump 102. For example, present embodiments may enable improved operation of the heat pump 102 in cold climate conditions (e.g., cold temperatures of the ambient environment 112) that may also coincide with increased demands for heating by the heat pump 102 (e.g., increase demand of the thermal load 110). As will be appreciated, in cold climate conditions, a discharge temperature and/or discharge superheat of the working fluid discharged by the compressor 130 may be greater than desired (e.g., in the heating mode of the heat pump 102) Accordingly, the heat pump 102 may operate to direct vapor working fluid and/or a vapor-liquid mixture of working fluid into the compressor 130 via the injection conduit 200 and injection port 140, which may cause cooling of working fluid within the compressor 130 and reduce the discharge temperature and/or superheat of the working fluid discharged by the compressor 130. The injected working fluid may also cause cooling of the compressor 130. In this way, the present techniques may enable improved operation of the heat pump 102 in cold climate conditions. For example, present embodiments enable improved operation of the heat pump 102 during periods of compressor 130 operation at greater pressure ratios.

In some embodiments, the disclosed techniques may enable an increase in operating efficiency of the compressor 130 and the heat pump 102. As will be appreciated, operation of the compressor 130 with greater efficiency may enable operation of the heat pump 102 with reduced energy consumption. Indeed, as discussed above, the controller 220 may adjust operation of the injection EEV 206 based on feedback from one or more of the sensors 226, whereby the feedback is indicative of the superheat or discharge temperature of the discharged working fluid. In some embodiments, the one or more sensors 226 may include a pressure transducer and a temperature sensor disposed along the discharge conduit 136, feedback from the pressure transducer and the temperature sensor may be received by the controller 220, and the controller 220 may determine a discharge temperature and/or superheat of the working fluid discharged by the compressor 130.

The controller 220 may control the injection EEV 206 such that the discharged working fluid achieves a particular discharge superheat or temperature (e.g., set point, set point value) and/or does not exceed a particular discharge superheat or discharge temperature (e.g., set point, set point value). A set point of the desired discharge superheat or discharge temperature may be based on a particular embodiment of the heat pump 102, a particular embodiment or type of the compressor 130, or other suitable parameter. In some embodiments, the set point of the desired discharge superheat or discharge temperature may be stored in the memory device 224. The controller 220 may be configured to receive feedback from one of the sensors 226 indicative of the discharge superheat or discharge temperature of the working fluid, compare the feedback to the set point (e.g., set point value) stored in the memory device 224, and adjust operation of the injection EEV 206 to cause the measured discharge superheat or discharge temperature to approach the set point discharge superheat or discharge temperature.

Additionally or alternatively, the injection conduit 200 and injection EEV 206 may be utilized and/or controlled to increase an operating capacity of the compressor 130, the first heat exchanger 104, the second heat exchanger 106, and/or the heat pump 102 generally. As mentioned above, the working fluid injected into the compressor 130 via the injection port 140 (e.g., secondary flow of working fluid) is combined with a primary flow of working fluid received via the suction port 134 in the compressor 130. Thus, a mass flow rate of working fluid discharged by the compressor 130 may be greater that a mass flow rate of working fluid received by the compressor 130 via the suction port 134. In some instances, the increase in mass flow rate of working fluid discharged by the compressor 130 may enable an increase in a heating capacity of the heat pump 102 (e.g., the first heat exchanger 104) in the heating mode of the heat pump 102. As will be appreciated, the increased heating capacity of the heat pump 102 (e.g., the first heat exchanger 104) in the heating mode may enable the heat pump 102 to satisfy greater heating loads in cold climates without utilization of an auxiliary heating system, such as a furnace that combusts a fuel to provide supplemental energy. In this way, present embodiments enable a reduction in the generation of greenhouse gas emissions.

It should be appreciated that techniques similar to those described above may be utilized during operation of the heat pump 102 in the cooling mode of the heat pump 102. In some instances, it may be desirable (e.g., based on feedback from the one or more sensors 226) to block flow of working fluid along the injection conduit 200 and therefore block injection of working fluid into the compressor 130 via the injection port 140. For example, at certain temperatures of the ambient environment 112, it may be desirable to block injection of working fluid into the compressor 130 via the injection port 140. In such instances, for example, the controller 220 may adjust the injection EEV 206 to a closed position. In other embodiments, the injection EEV 206 may include a fixed orifice or capillary tube and a solenoid valve, and the solenoid valve may be adjusted to a closed position to block working fluid flow to the injection port 140. At other temperatures of the ambient environment 112 (e.g., higher temperatures), it may be desirable to enable injection of working fluid into the compressor 130 via the injection port 140.

In some embodiments, one of the sensors 226 may be configured to detect a temperature of the ambient environment 112 and provide feedback indicative of the temperature to the controller 220. The controller 220 may compare the feedback indicative of the temperature to a set point temperature (e.g., stored in the memory device 224) and adjust a position of the injection EEV 206 based on the comparison. For example, the set point temperature may be approximately 90 degrees Fahrenheit. In response to a determination that the temperature of the ambient environment 112 is at or above the set point temperature, the controller 220 may adjust the injection EEV 206 toward an open position to enable injection of working fluid into the compressor 130 via the injection port 140. In response to a determination that the temperature of the ambient environment 112 is below the set point temperature, the controller 220 may adjust the injection EEV 206 toward a closed position to block injection of working fluid into the compressor 130 via the injection port 140. Additionally or alternatively, in the cooling mode, the controller 220 may control and/or adjust a position of the injection EEV 206 (e.g., based on feedback from one or more of the sensors 226) to achieve a desired discharge superheat and/or discharge temperature, in the manner similarly described above.

FIG. 7 illustrates a room temperature control scheme 250 for an HVAC system (e.g., HVAC system 100). The control scheme 250 receives a temperature set point 252 via a thermostat 254. For example, a user may input a desired temperature into a user interface of the thermostat 252. The thermostat 252 receives an actual temperature 254 of a conditioned space 256 (e.g., from a temperature sensor) and compares the actual room temperature 254 to the temperature set point 250. The difference 258 between the temperature set point 250 and the actual room temperature 254 (e.g., error) is fed to a thermostat controller 260. The thermostat controller 260 converts the difference 258 into a thermostat control signal 262, which may correspond to input(s) for systems and processes of a vapor compression system 72. As noted above, in the describe embodiment, the thermostat 252 is a communicating thermostat configured to communicate with components of the vapor compression system 72 (e.g., via digital signals). In other embodiments, the thermostat 252 may be a non-communicating (e.g., conventional) thermostat configured to output one or more simple activation signals (e.g., 24V signals) to call for conditioning.

As discussed above, the vapor compression system 72 includes an evaporator. Various subsystems of the vapor compression system 72, including the compressor, the EEV, the injection EEV, and the outdoor fan may affect a temperature of the evaporator (e.g., temperature of refrigerant in the evaporator). As the evaporator exchanges heat with an airflow into the conditioned space, the actual room temperature 254 changes based on an evaporator temperature 268. The control scheme 250 includes a room temperature sensor 270 configured to measure the actual room temperature 254, which is communicated to the thermostat 252 as a feedback signal 272.

Due to thermal inertia of the conditioned space 256, the actual room temperature 254 may respond relatively slowly to changes in the temperature set point 250. In contrast, the vapor compression system 72 may include controllable processes whose parameters respond much faster to changing inputs. Present embodiments are directed to techniques of controlling these controllable processes in separate control loops cycling at a faster rate than the room temperature control scheme 250. FIG. 8 illustrates four control loops of the vapor compression system 72, including a compressor control loop 290 for controlling the compressor speed, an EEV control loop 292 for controlling the EEV position, an injection EEV control loop 294 for controlling the injection EEV 206, and an outdoor fan control loop 296 for controlling the outdoor fan speed. Each of the compressor 130, the EEV 120, the injection EEV 206, and the fan 118 are controlled by their respective control loops based on respective input signals. Outputs of these control loops may respond to the input signals quickly compared to the response of the actual room temperature 254 to the temperature set point 250.

FIG. 9 is a schematic of the compressor control loop 290 (e.g., second feedback control loop) nested within a room control loop 300 (e.g., first feedback control loop) controlled by a communicating thermostat 302, in accordance with an embodiment of the present disclosure. FIG. 10 is a schematic of the room control loop 300 of FIG. 9, wherein the communicating thermostat 302 operates to determine a difference 304 between the temperature set point 250 and the actual room temperature 254 and operates to transform the resulting error term into a control signal 306 corresponding to a target evaporator temperature 308 via a room temperature controller 310 (e.g., PI or PID controller). The control signal 306 produced by the room temperature controller 310 of the communicating thermostat 302 may be a digital signal corresponding to the target evaporator temperature 308 as a continuous variable across a range of values. The room temperature controller 310 of the communicating thermostat 302 may include a proportional, integral, and/or derivative component. The target evaporator temperature 308 is fed as an input into the compressor control loop 290, which is depicted in FIG. 11.

The compressor control loop 290 receives the target evaporator temperature 308 as a set point for the evaporator 80. Then, the compressor control loop 290 determines a difference 332 between the target evaporator temperature 308 and an actual evaporator temperature 334. The resulting error term is transformed by a compressor speed controller 336 (e.g., PID controller) into a compressor control signal 338 corresponding to a compressor speed 340. The compressor control signal 338 may be adjusted based on one or more compressor protection mechanisms 342 (e.g., limit conditions) designed to protect the compressor 74 from faults. For example, the compression protection mechanisms 342 may limit the compressor speed based on a maximum pressure, a minimum pressure, a discharge temperature, a freezing point, and/or a current associated with the compressor. Then, the compressor control signal 338 may instruct the compressor 74 to operate at a compressor speed responsive to the target evaporator temperature 308. The compressor speed, in turn, directly affects the actual evaporator temperature 334, which is measured (e.g., via a temperature sensor) and communicated back to the compressor speed controller 336 as a feedback signal.

The room control loop 300 includes the thermostat 302 configured to determine a difference between the thermostat set point 250 (e.g., input signal, reference signal) and the actual temperature 254 of the conditioned space 256 (e.g., room). Based on the difference 304 (e.g., error), the room temperature controller 310 (e.g., PID controller) of the room control loop 300 produces the control signal 306 (e.g., call for cooling) representing an amount of cooling requested of the vapor compression system 72. Specifically, the amount of cooling may correspond to the target evaporator temperature 308. The target evaporator temperature 308 may be an input or a set point for various processes and systems of the vapor compression system 72. For example, the target evaporator temperature 308 may be used as an input signal for the compressor control loop 290 to control the compressor speed. As the vapor compression system 72 (e.g., compressor, evaporator) works to cool the conditioned space 256 according to the target evaporator temperature 308, the thermostat 302 receives the actual room temperature 254 as a feedback signal to the thermostat controller 310.

In some embodiments, the thermostat 302 may be a non-communicating thermostat and issues associated with working with the non-communicating thermostat may be addressed using techniques such as those disclosed in U.S. Pat. No. 11,644,213, which is hereby incorporated by reference in its entirety. The non-communicating thermostat may not communicate directly with the compressor 74 to deliver the target evaporator temperature 308. Instead, the non-communicating thermostat may generate an activation signal (e.g., 24V signal) as a call for conditioning. In a two-stage system, the thermostat 302 may generate a first activation signal (e.g., Y1) to call for a first cooling stage, and the thermostat may generate a second activation signal (e.g., Y2) to call for a second cooling stage. The first activation signal and the second activation signal may each correspond initially to a respective predetermined set point evaporator temperature. For example, if the compressor 74 receives the first activation signal (e.g., Y1), then the set point evaporator temperature may initially be set to a first predetermined value (e.g., 50° F.) corresponding to the first cooling stage. If the compressor 74 receives the second activation signal (e.g., Y1+Y2), then the set point evaporator temperature may be initially set to a second predetermined value (e.g., 40° F.) corresponding to the second cooling stage. In this way, the compressor control loop may function as a virtual thermostat, setting the set point evaporator temperature. In some cases, the set point evaporator temperature may change based on a time elapsed before convergence of the evaporator temperature to the set point evaporator temperature. It should be noted that the predetermined values (e.g., the first predetermined value and/or the second predetermined value) may be based on historical data (e.g., average operating temperature measured over time), manually set, a last measured operating temperature, or the like.

Whether the thermostat 302 is a communicating thermostat or a non-communicating thermostat, the set point evaporator temperature 308 is received by the compressor control loop 290 and compared to the actual evaporator temperature 334 to determine the error term 332. The compressor speed controller 336 (e.g., PID controller) produces the compressor control signal 338 based on the error term 332. As mentioned above, the compressor control loop cycles 290 faster than the room control loop 300 because the compressor speed and the evaporator temperature have less thermal inertia and respond faster to one another than the room temperature of the conditioned space 256. As a result, the faster compressor control loop 290 may include protection mechanisms 342 that respond quickly to potential fault conditions in the compressor 74.

FIG. 12 illustrates the EEV control loop 292 for controlling an EEV position 358. The EEV control loop 292 receives a suction superheat (SSH) set point 360 based on an outdoor ambient temperature and/or the compressor speed. For example, a control unit of the outdoor unit may monitor the outdoor ambient temperature and the compressor speed and determine the SSH set point 360 based on a predetermined relationship between the outdoor ambient temperature, the compressor speed, and the SSH set point 360. As such, the EEV control loop 292 may be selectively coupled to the compressor control loop 290. The EEV control loop 292 may determine an actual SSH 362 at the EEV 120 based on measurements provided by a temperature sensor and a pressure sensor downstream of the EEV 120. The saturation temperature of the refrigerant may be derived from the measured temperature, the measured pressure, and known data for the relevant fluid (e.g., known refrigerant boiling points). Further, the SSH 362 may be calculated as the difference between the measured temperature and the saturation temperature. In other words, the SSH 362 is a measure of degrees above the boiling point of the refrigerant at the EEV 120. The EEV control loop 292 may determine a difference 364 between the SSH set point 360 and the actual SSH 362. The resulting error term is input to an EEV position controller 366 (e.g., PID controller) to generate an EEV control signal 368 to move (e.g., open or close) the EEV 120 to a position. The EEV position 358 may, in turn, affect the SSH 362 at the EEV 120, the evaporator temperature, and other parameters of the vapor compression system 72. The EEV control loop 292 may further include EEV protection mechanisms 370 (e.g., EEV position limits) configured to keep the EEV 120 open past a minimum number of steps. The minimum number of steps may change as a function of the outdoor ambient temperature.

FIG. 13 illustrates the injection EEV control loop 294 for controlling an injection EEV position 400. The injection EEV control loop 294 receives a discharge superheat (DSH) set point 402 based on the outdoor ambient temperature and/or the compressor speed. For example, the control unit of the outdoor unit may monitor the outdoor ambient temperature and the compressor speed and determine the DSH set point 402 based on a predetermined relationship between the outdoor ambient temperature, the compressor speed, and the DSH set point 402. As such, the injection EEV control loop 294 may be selectively coupled to the compressor control loop 290. The injection EEV control loop 294 may determine the actual DSH 404 at the injection EEV 206 based on measurements provided by a temperature sensor and a pressure sensor downstream of the injection EEV 206. The saturation temperature of the refrigerant may be derived from the measured temperature, the measured pressure, and known data for the relevant fluid (e.g., known refrigerant boiling points). Further, the DSH 404 may be calculated as the difference between the measured temperature and the saturation temperature. In other words, the DSH 404 is a measure of degrees above the boiling point of the refrigerant at the injection EEV 206. The injection EEV control loop 294 may determine a difference 406 between the DSH set point 402 and the actual DSH 404. The resulting error term is input to an injection EEV position controller 408 (e.g., PID controller) to generate an injection EEV control signal 410 to move (e.g., open or close) the injection EEV 206 to a position. The injection EEV position 400 may, in turn, affect the DSH 404 at the injection EEV 206, the evaporator temperature, and other parameters of the vapor compression circuit 72. The injection EEV control loop 294 may further include injection EEV protection mechanisms 412 (e.g., injection EEV position limits) configured to keep the injection EEV within an acceptable range of positions. The acceptable range of positions change based on the outdoor ambient temperature.

FIG. 14 illustrates a fan control loop 296 for controlling a speed 440 (e.g., PWM) of an outdoor fan. The fan control loop 296 receives a pressure set point 442 for refrigerant in an outdoor coil (e.g., condenser). The pressure set point 442 may be controlled by a control unit (e.g., control panel) based on the outdoor ambient temperature and the compressor speed. As such, the fan control loop 296 may be selectively coupled to the compressor control loop 290. Additionally, the fan control loop 296 may determine a current pressure 444 (e.g., via a pressure sensor) of the outdoor coil. A difference 446 between the set point pressure and the current pressure (e.g., error) is input to a fan controller 448 (e.g., PID controller) configured to convert the error term into a fan control signal 450 (e.g., PWM signal) for operating a fan (e.g., fan 118) at the desired fan speed 440. The fan speed 440 may affect the current pressure 444, the outdoor coil temperature, the evaporator temperature, the SSH 362, and/or the DSH 404. Furthermore, the fan control loop 296 may include fan protection mechanisms 452 (e.g., fan speed limits) to prevent the fan control signal 450 from causing a fault in the fan system. The fan protection mechanisms 452 may include upper and lower speed limits that vary based on the outdoor ambient temperature. Additionally, the fan protection mechanisms 452 may adjust the fan speed 440 to maintain the current pressure 444 between predetermined high and low pressure limits.

Although FIGS. 7-15 are described above with respect to an HVAC system in a cooling mode, it should be recognized that similar techniques may be applied to a heat pump system in a heating mode, a dehumidification mode, or a boost mode. For example, in a heating mode, the room control loop may output a control signal corresponding to a target condenser temperature (e.g., set point condenser temperature). Likewise, the set point evaporator temperature and the actual evaporator temperature may be replaced with a set point condenser temperature and an actual condenser temperature. Furthermore, depending on whether the heat pump system is in the cooling mode or the heating mode, the EEV control loop may control the position of a first EEV or a second EEV.

As described in detail above, present embodiments are directed to a control scheme for HVAC systems operable in a variable capacity mode utilizing a communicating thermostat or a non-communicating thermostat. The control scheme includes independent feedback control loops (e.g., PID control schemes) for controlling operating parameters including a compressor speed, an EEV position, an outdoor fan sped, and an injection EEV position.

The compressor speed is controlled using a compressor control loop (e.g., inner loop) nested within a room control loop (e.g., outer loop). The room control loop monitors a temperature of a conditioned space (e.g., room) and compares the temperature to a desired set point temperature. The room control loop may utilize a controller (e.g., PID controller) to output a demand signal as an input to the compressor control loop. The compressor speed control loop outputs a compressor control signal that takes into account the limitations of the refrigeration system based on certain operating conditions (e.g., ambient temperature). In this way, the compressor speed control loop protects the refrigeration system from tripping or faulting and at the same time tries to match the capacity demanded by the room control loop.

For a communicating system, the room control loop has the room temperature as the control variable and the set point temperature as a target. These variables feed into a PID controller which outputs a target demand for the compressor control loop. This target demand feeds the compressor control loop as a target while the control variable is the current demand. The difference between the target demand and the current demand feeds a PID controller outputting a new capacity. This new capacity will affect the room temperature which will be used again for the outer loop, repeating this process again until both PIDs have reached their target. The demand signal is converted to a compressor speed signal after passing one or more compressor protection mechanisms.

For a non-communicating system, the room control loop assumes a target to the variable that can be read and controlled. The target may be adjusted after a period of time before the variable converges to the target. When the HVAC system is operating in cooling mode, the target is the evaporating temperature or pressure and the current evaporating temperature or pressure is the variable to be monitored. Based on the difference between the evaporating temperature or pressure and the current evaporating temperature or pressure, the PID loop outputs a demand signal to the compressor control loop. The compressor control loop compares the target to the current demand, performs additional checks to avoid trips and faults, and output a new compressor speed. This new compressor speed affects the evaporating pressure or temperature that is the input signal for the room control loop. The room control loop may adjust the target again, repeating the cycle until the target is achieved for both loops. The room control loop target may be adjusted based on compressor speed changes over time. For example, if the compressor speed does not decrease over time, it may be inferred that the room temperature is not converging to the temperature set point. Then, the target may be changed to a new target.